Frequency synthesizer with loop filter calibration for bandwidth control

Abstract

According to one exemplary embodiment, a frequency synthesizer module includes a loop filter, where the loop filter includes a capacitor having a first terminal and a second terminal. The frequency synthesizer module further includes a loop filter calibration module coupled to the capacitor in the loop filter. The loop filter calibration module causes an initial capacitance between the first terminal and the second terminal of the capacitor to increase to a target capacitance when the loop filter is in a calibration mode. The target capacitance can causes in increase in control of a bandwidth of the loop filter and a reduction in percent error of a unity gain bandwidth of the loop filter. The loop filter further includes a switched capacitor array configured to cause the initial capacitance to increase to the target capacitance in response to a digital feedback signal provided by the loop filter calibration module.

1. A frequency synthesizer module comprising:
 a loop filter, said loop filter comprising a capacitor having a first terminal and a second terminal; 
 a loop filter calibration module coupled to said capacitor in said loop filter; 
 wherein said loop filter calibration module causes an initial capacitance between said first terminal and said second terminal of said capacitor to increase to a target capacitance when said loop filter is in a calibration mode, wherein said capacitor is disconnected from said loop filter when said loop filter is in said calibration mode. 
 
   
   
     2. The frequency synthesizer module of  claim 1  wherein said target capacitance causes a reduction in percent error of a unity gain bandwidth of said loop filter. 
   
   
     3. The frequency synthesizer module of  claim 1  wherein said loop filter further comprises a switched capacitor array coupled between said first terminal and said second terminal of said capacitor, wherein said switched capacitor array is configured to cause said initial capacitance to increase to said target capacitance in response to a digital feedback signal provided by said loop filter calibration module. 
   
   
     4. The frequency synthesizer module of  claim 1  wherein said target capacitance causes an increase in control of a bandwidth of said loop filter. 
   
   
     5. The frequency synthesizer module of  claim 1  wherein said loop filter calibration module comprises an oscillator, wherein said oscillator provides a sawtooth waveform at said first terminal of said capacitor when said loop filter is in said calibration mode. 
   
   
     6. The frequency synthesizer module of  claim 3  wherein said loop filter calibration module comprises a binary search block, wherein said binary search block is configured to receive a digital voltage error signal and output said digital feedback signal. 
   
   
     7. The frequency synthesizer module of  claim 6  wherein said loop filter calibration module further comprises a phase error to voltage error converter coupled to said binary search block, wherein said phase error to voltage error converter is configured to receive up and down phase error signals and output said digital voltage error signal. 
   
   
     8. The frequency synthesizer module of  claim 1  further comprising a voltage controlled oscillator module coupled to said loop filter, wherein said voltage controlled oscillator module is configured to generate an output signal in response to a tuning voltage outputted by said loop filter. 
   
   
     9. The frequency synthesizer module of  claim 8  further comprising a divider module coupled to said voltage controlled oscillator module, wherein said divider module is configured to receive said output signal from said voltage controlled oscillator module, divide said output signal by a number than is greater than zero and less than one, and output a feedback signal. 
   
   
     10. The frequency synthesizer module of  claim 1  wherein said frequency synthesizer module comprises a Gaussian minimum shift keying modulated frequency synthesizer. 
   
   
     11. A loop filter calibration module coupled to a loop filter in a frequency synthesizer module, said loop filter calibration module comprising:
 an oscillator, said oscillator coupled to a capacitor in said loop filter, said oscillator being configured to generate an output signal having a sawtooth waveform; 
 wherein said loop filter calibration module causes an initial capacitance between a first terminal and a second terminal of said capacitor to increase to a target capacitance when said loop filter is in a calibration mode. 
 
   
   
     12. The loop filter calibration module of  claim 11  wherein said capacitor is disconnected from said loop filter when said loop filter is in said calibration mode. 
   
   
     13. The loop filter calibration module of  claim 11  wherein said target capacitance causes a reduction in percent error of a unity gain bandwidth of said loop filter. 
   
   
     14. The loop filter calibration module of  claim 11  wherein said loop filter further comprises a switched capacitor array coupled between said first terminal and said second terminal of said capacitor, wherein said switched capacitor array is configured to cause said initial capacitance to increase to said target capacitance in response to a digital feedback signal provided by said loop filter calibration module. 
   
   
     15. The loop filter calibration module of  claim 11  wherein said target capacitance causes an increase in control of a bandwidth of said loop filter. 
   
   
     16. The loop filter calibration module of  claim 11  further comprising a phase/frequency detector coupled to said oscillator, wherein said phase/frequency detector is configured to receive said output signal from said oscillator and a reference signal and output an up phase error signal and a down phase error signal. 
   
   
     17. The loop filter calibration module of  claim 16  further comprising a phase error to voltage error converter coupled to said phase/frequency detector, wherein said phase error to voltage error converter is configured to receive and convert said up phase error signal and said down phase error signal to a voltage error signal. 
   
   
     18. The loop filter calibration module of  claim 17  further comprising a binary search block coupled to said phase error to voltage error converter, wherein said binary search block is configured to receive said voltage error signal and output a digital feedback signal to said loop filter. 
   
   
     19. The loop filter calibration module of  claim 11  wherein said loop filter further comprises a resistor coupled to said capacitor, wherein said resistor is disconnected from said capacitor in said calibration mode. 
   
   
     20. The loop filter calibration module of  claim 11  wherein said frequency synthesizer comprises a modulated frequency synthesizer. 
   
   
     21. A frequency synthesizer module comprising:
 a loop filter, said loop filter comprising a capacitor having a first terminal and a second terminal; 
 a loop filter calibration module coupled to said capacitor in said loop filter, said loop filter calibration module comprising an oscillator; 
 wherein said loop filter calibration module causes an initial capacitance between said first terminal and said second terminal of said capacitor to increase to a target capacitance when said loop filter is in a calibration mode, wherein said oscillator provides a sawtooth waveform at said first terminal of said capacitor when said loop filter is in said calibration mode.